1. Field of the Invention
The present invention generally relates to a method for forming a pattern. More particularly, the present invention relates to a method for forming a pattern capable of reducing the stress of a film, and a method for forming a thin film transistor using said method.
2. Description of Related Art
The display apparatus is the communication interface between user and information media. Currently, the flat panel display is the trend in development. The flat panel display mainly includes organic electro-luminescence display (OELD), plasma display panel (PDP), thin film transistor liquid-crystal display (TFT-LCD) and so on. The TFT-LCD is in widespread use.
The TFT-LCD is composed of a thin film transistor (TFT) array substrate, a color filter (CF) array substrate and a liquid crystal (LC) layer. The TFT array substrate comprises a plurality of pixel units arranged in an array. Each pixel unit is composed of a thin film transistor (TFT), data lines, scan lines and a pixel electrode. The data lines, scan lines and the pixel electrode are electrically connected to the thin film transistor. The above mentioned thin film transistor, which serves as a switch device of the pixel unit, comprises a gate, a channel layer, and a source/drain.
In the conventional fabrication process of the thin film transistor, the film fabrication process, the photolithography process, the etching process and so on are used to form the above mentioned gate, channel layer, source/drain. The presence of uneven stress would occur in each film. Especially, the uneven stress would occur between different layers, which have the large difference in thermal expansion coefficient, after a high temperature process, and therefore the substrate is severely warped. It means that the adhesion between the film and the substrate, or between different films is poor, such that the film would peel. Besides, during the photolithography process, the misalignment and exposure shifting would occur due to the warped substrate.
It should be noted that with the development of the large-sized LCD, the fabrication process of large-sized films becomes more and more important. However, the problem caused by the uneven stress between the films becomes more and more serious with the increased size of the film, and therefore the development of the large-sized LCD TV would be limited.